1. Field of the Invention
This invention relates to a grinder pump, and more particularly to a grinder pump of the water immersed type which functions both as a pump and a grinder to pump liquid and concurrently grind or shred foreign material contained in the flowing liquid.
2. Description of the Related Art
A typical grinder pump which has been conventionally known in the art is disclosed in U.S. Pat. No. 4,454,993 issued to Tomoyuki Shibata et al on June 19, 1984 and assigned to the assignor of the application. The grinder pump is constructed in a manner such that a grinder ring is fitted in a pump casing and covered at the lower portion thereof by a suction cover, and the grinder ring, pump casing and suction cover are integrally held by bolts.
However, in the conventional grinder pump, because the grinder ring is rapidly worn due to the grinding or shredding of solid material contained in liquid to be pumped, it is required to frequently carry out the replacement of the grinder ring. Such replacement of the grinder ring is carried out by first removing the suction cover from the pump casing and removing the grinder ring from the pump casing. However, the removal of the grinder ring from the pump casing is highly troublesome and requires much time and labor, because the grinder ring is rigidly fixed in the pump casing.
Grinder pumps can be classified into two types. A first is the "resuction" type in which solid materials or woven fabric materials entrained in pumped liquid are repeatedly reciprocated vertically through a duct defined by the pump shroud into the grinder mechanism until they are completely passed upward or reduced in size and fall to an inaccessible area. An example of such a resuction type of grinder pump can be found in U.S. Pat. No. 3,667,692 (Reissue no. 28,104). In the Grace patent, solid materials are sucked up through an inlet duct to a comminutor or impeller disk. The solid materials or woven fabric materials are repeatedly reciprocated through the duct and onto the impeller disk until they are either completely passed upward or reduced in size and fall to an inaccessible portion of the bottom of the container within which the grinder pump is positioned. The shroud, together with the smooth internal surface of the comminutor ring constitute a duct which provides a guide for the smooth reciprocation of fluid and particulate matter therethrough. In the resuction type grinder, such as that of Grace, the need for a shroud thus provides an element which can be used for clamping a grinder ring into a pump casing.
However, there is a second type or "release" type of grinder pump which does not require a guide duct. Since the prolonged comminuting of solid or fabric material can cause fairly rapid wear of the comminutor blades, the release type of grinder pump provides a comminutor which serves more as a strainer than a comminutor. However, because of the lack of a shroud, it is difficult to provide clamping of the comminutor ring onto the pump body as is done in Grace.
Accordingly, it is desirable that a release type grinder pump be developed which is capable of readily carrying out the detachable fitting of a grinder ring with respect to a pump casing in order to facilitate the replacement of the grinder ring and the like.